The present invention concerns systems and methods for gathering data and information from a plurality of distributed devices and correctly aggregating the collected or gathered data in a time-consistent manner.
Many electronic systems comprise a plurality of spread devices, i.e. devices which can be distributed over an extensive area, and wherefrom data concerning operation thereof must be collected and aggregated in a time-consistent manner, e.g. for monitoring purposes.
Examples of such systems comprise, but are not limited to renewable energy power generation plants, such as photovoltaic installations, wind farms and the like. Further examples of such systems are for instance rectifier networks for telecommunication. The spread devices can typically be electric converters, such as rectifiers, inverters and the like.
A serial line, e.g. an RS485 serial line, or another low-speed communication or transmission channel is often used to connect the spread electronic devices to a master device, which monitors the system. A low-speed transmission channel is usually chosen in these applications in view of the long distances which must be covered, sometimes spanning over several kilometers. A master-slave approach is usually adopted for transmitting data from the spread devices (slave devices or slave units) to a control unit or master device, acting as a data logger controller. This latter collects the measured values of one or more parameters from each slave device and relating to the operation of the slave devices or apparatus connected thereto. Measured parameters of interest can include, but are not limited to, power, energy, voltage, temperature of device components, and the like. These parameters are usually time-variable parameters, i.e. they vary during time.
The data transmission protocol between data logger controller, i.e. master device, and slave devices can sometimes be very simple, such that the measured value of not more than a single parameter can be transmitted at a time. As such, if e.g. 50 different parameter values shall be gathered from the slave devices, the master device shall send a total of fifty data polling commands per each single slave device. If there is a total of 64 such devices, and each transaction, i.e. polling command from the master device and answer from the slave device to the master device requires 200 ms, the total time required for completing the data gathering is 10.6 minutes. The collected data are not time-consistent and synchronous, and a delay up to 10.6 minutes exists between the first to the last value collected by the master device.
Methods also exist, wherein a single message is configured to transmit several parameters together, but sometime this is still not enough, because of the large amount of measurement data that require to be transferred. Several messages are still required to transfer a complete set of measurements. Additionally the gathered data from the various devices will be non-synchronous.
Assuming for instance that the slave devices are micro-inverters connecting a plurality of photovoltaic panels or wind-power generators to an electric power distribution grid, and assuming that information is required from the master unit on the total instant power generated by the entire set of micro-inverters, a standard system which uses a low-speed transmission channel as described above would not be able to determine the instant power generated at a given point in time, since what is actually gathered by the master device is the sum of data sampled at different time instants, spread over more than ten minutes.
In order to synchronize measurements of parameters, some known systems utilize to time stamps to tag the measurements, performed at different instants in time. This approach requires the monitoring system to provide a reference clock in order to synchronize the various slave devices. Other approaches provide for speeding-up the polling period, in order to reduce the poll time down to seconds, using a fast connection between the slave devices and the master device. Both systems are costly and complex and moreover are not back-compatible i.e. cannot be implemented in already existing installations.
A need therefore exists for a system and method of gathering data relating to time-variable parameters from a plurality of devices connected to a master or data logger controller, which is simple and enables gathering time-consistent, synchronized data.